//! Walker-driven highlighting (ADR-0024 §migration Phase F).
//!
//! `highlight_runs(source)` returns the per-byte highlight class
//! assignments for every token shape in `source`. It is the
//! single entry point that consumers (input panel, echo lines)
//! should use to colour DSL input — there is no separate lexer
//! pre-pass.
//!
//! Strategy:
//!
//! - Try the walker first. Whatever it consumed end-to-end (entry
//!   word + matching nodes) contributes `WalkResult::per_byte_class`.
//! - For any bytes the walker did not cover — input the walker
//!   doesn't engage on at all (no registered entry word), trailing
//!   junk after a partial match, or content past a structural
//!   failure — fall back to a byte-shape scanner that classifies
//!   each consumed token by its shape using the same `lex_helpers`
//!   primitives the walker uses internally.
//!
//! The two streams are returned in source-byte order; whitespace
//! gaps are not represented (the renderer fills them with the
//! default foreground colour).

use crate::dsl::grammar::HighlightClass;
use crate::dsl::walker::context::WalkContext;
use crate::dsl::walker::lex_helpers::{
    consume_bare_path, consume_flag, consume_ident, consume_number_literal,
    consume_string_literal, skip_whitespace,
};
use crate::dsl::walker::outcome::{ByteClass, WalkBound};

/// Produce the per-byte highlight classes for `source`.
///
/// Defaults to `Mode::Simple`. Callers in advanced-mode UIs
/// should use [`highlight_runs_in_mode`] so SQL keywords get
/// matched and highlighted past the entry word (the simple-mode
/// gate at the dispatcher truncates the walker on advanced-only
/// commands, ADR-0030 §2).
#[must_use]
pub fn highlight_runs(source: &str) -> Vec<ByteClass> {
    highlight_runs_in_mode(source, crate::mode::Mode::Simple)
}

/// Mode-aware [`highlight_runs`] (ADR-0032 §10.6 follow-up).
///
/// In `Mode::Advanced` the walker matches every Phase-2 SQL
/// token, producing the keyword classes the renderer needs to
/// colour `select` / `from` / `where` / `union` / `case` / etc.
#[must_use]
pub fn highlight_runs_in_mode(
    source: &str,
    mode: crate::mode::Mode,
) -> Vec<ByteClass> {
    let mut ctx = WalkContext::new();
    ctx.mode = mode;
    let (result, _cmd) = super::walk(source, WalkBound::EndOfInput, &mut ctx);
    let mut classes: Vec<ByteClass> = result
        .map(|r| r.per_byte_class)
        .unwrap_or_default();

    let scan_start = classes.last().map_or(0, |c| c.end);
    scan_remainder(source, scan_start, &mut classes);
    classes
}

/// Byte-shape scan from `start` to end of source, appending each
/// classified token to `classes`. Whitespace gaps are skipped.
fn scan_remainder(source: &str, start: usize, classes: &mut Vec<ByteClass>) {
    let bytes = source.as_bytes();
    let mut pos = start;
    while pos < bytes.len() {
        pos = skip_whitespace(source, pos);
        if pos >= bytes.len() {
            break;
        }
        let b = bytes[pos];
        // Identifier first — covers keywords-by-shape, since at
        // the highlight layer we no longer distinguish keyword from
        // identifier without a successful walker match.
        if (b.is_ascii_alphabetic() || b == b'_')
            && let Some((s, e)) = consume_ident(source, pos)
        {
            classes.push(ByteClass {
                start: s,
                end: e,
                class: HighlightClass::Identifier,
            });
            pos = e;
            continue;
        }
        if b == b'\'' {
            // Quoted string. Unterminated → mark the rest as Error
            // so the user sees the unclosed run highlighted.
            if let Some(((s, e), _)) = consume_string_literal(source, pos) {
                classes.push(ByteClass {
                    start: s,
                    end: e,
                    class: HighlightClass::String,
                });
                pos = e;
            } else {
                classes.push(ByteClass {
                    start: pos,
                    end: bytes.len(),
                    class: HighlightClass::Error,
                });
                pos = bytes.len();
            }
            continue;
        }
        if b == b'-' && bytes.get(pos + 1) == Some(&b'-') {
            // Flag. `--` without a body is BadFlag → Error.
            if let Some((s, e)) = consume_flag(source, pos) {
                classes.push(ByteClass {
                    start: s,
                    end: e,
                    class: HighlightClass::Flag,
                });
                pos = e;
            } else {
                classes.push(ByteClass {
                    start: pos,
                    end: pos + 2,
                    class: HighlightClass::Error,
                });
                pos += 2;
            }
            continue;
        }
        let looks_like_number = b.is_ascii_digit()
            || (b == b'-'
                && bytes
                    .get(pos + 1)
                    .copied()
                    .is_some_and(|c| c.is_ascii_digit()));
        if looks_like_number
            && let Some((s, e)) = consume_number_literal(source, pos)
        {
            classes.push(ByteClass {
                start: s,
                end: e,
                class: HighlightClass::Number,
            });
            pos = e;
            continue;
        }
        if matches!(b, b':' | b'(' | b')' | b',' | b'=' | b'.') {
            classes.push(ByteClass {
                start: pos,
                end: pos + 1,
                class: HighlightClass::Punct,
            });
            pos += 1;
            continue;
        }
        // Bare-path tail (e.g., trailing `frobulate widgets` past
        // a partial command match): only used when we know the
        // remainder isn't structured. Without a grammar context
        // here we conservatively treat as Error so the user sees
        // the unknown-shape byte highlighted.
        //
        // For multi-byte UTF-8 (emoji, unknown unicode) advance
        // one whole codepoint as Error.
        let ch = source[pos..]
            .chars()
            .next()
            .expect("pos < bytes.len() ⇒ at least one char");
        let len = ch.len_utf8();
        // If the char is alphanumeric (unusual at this fall-through
        // — should already have been caught above), classify as
        // Identifier-ish. Otherwise Error.
        let class = if ch.is_ascii_alphanumeric() || ch == '_' {
            HighlightClass::Identifier
        } else if ch.is_whitespace() {
            // Whitespace is filtered above; this branch is unreachable
            // in practice.
            pos += len;
            continue;
        } else {
            HighlightClass::Error
        };
        let _ = consume_bare_path; // silence unused-import lint when not exercised
        classes.push(ByteClass {
            start: pos,
            end: pos + len,
            class,
        });
        pos += len;
    }
}

#[cfg(test)]
mod tests {
    use super::*;

    fn run(input: &str) -> Vec<(usize, usize, HighlightClass)> {
        highlight_runs(input)
            .into_iter()
            .map(|c| (c.start, c.end, c.class))
            .collect()
    }

    #[test]
    fn empty_input_yields_no_runs() {
        assert!(highlight_runs("").is_empty());
        assert!(highlight_runs("   ").is_empty());
    }

    #[test]
    fn entry_keyword_classified_as_keyword() {
        assert_eq!(run("quit"), vec![(0, 4, HighlightClass::Keyword)]);
    }

    #[test]
    fn keyword_plus_identifier_via_walker() {
        // `show data Customers` walks end-to-end.
        let runs = run("show data Customers");
        assert_eq!(
            runs,
            vec![
                (0, 4, HighlightClass::Keyword),
                (5, 9, HighlightClass::Keyword),
                (10, 19, HighlightClass::Identifier),
            ],
        );
    }

    #[test]
    fn unknown_command_word_classified_by_byte_shape() {
        // Walker doesn't engage; fallback classifies as Identifier.
        assert_eq!(run("frobulate"), vec![(0, 9, HighlightClass::Identifier)]);
    }

    #[test]
    fn unknown_chars_classified_as_error() {
        assert_eq!(run("$"), vec![(0, 1, HighlightClass::Error)]);
    }

    #[test]
    fn unterminated_string_classified_as_error_through_to_eof() {
        assert_eq!(run("'oops"), vec![(0, 5, HighlightClass::Error)]);
    }

    #[test]
    fn string_literal_classified() {
        assert_eq!(run("'hello'"), vec![(0, 7, HighlightClass::String)]);
    }

    #[test]
    fn flag_classified_via_fallback() {
        // Walker doesn't engage for a bare `--all-rows`.
        assert_eq!(
            run("--all-rows"),
            vec![(0, 10, HighlightClass::Flag)],
        );
    }

    #[test]
    fn bare_double_dash_classified_as_error() {
        assert_eq!(run("--"), vec![(0, 2, HighlightClass::Error)]);
    }

    #[test]
    fn number_classified_via_fallback() {
        assert_eq!(run("42"), vec![(0, 2, HighlightClass::Number)]);
        assert_eq!(run("-5"), vec![(0, 2, HighlightClass::Number)]);
        assert_eq!(run("3.14"), vec![(0, 4, HighlightClass::Number)]);
    }

    #[test]
    fn punct_classified_via_fallback() {
        // Bare `:` outside any walker context.
        assert_eq!(run(":"), vec![(0, 1, HighlightClass::Punct)]);
    }

    #[test]
    fn trailing_tokens_after_partial_walk_are_byte_scanned() {
        // `quit nonsense` — walker matches `quit`, then trailing
        // `nonsense` is fallback-classified.
        let runs = run("quit nonsense");
        assert_eq!(
            runs,
            vec![
                (0, 4, HighlightClass::Keyword),
                (5, 13, HighlightClass::Identifier),
            ],
        );
    }

    #[test]
    fn whitespace_gaps_are_not_represented_as_runs() {
        // Two whitespace-separated tokens produce exactly two
        // class spans; the renderer fills the gap with fg.
        let runs = run("show  table");
        assert_eq!(runs.len(), 2);
        assert_eq!(runs[0].2, HighlightClass::Keyword);
        assert_eq!(runs[1].2, HighlightClass::Keyword);
    }

    #[test]
    fn full_command_walks_with_each_class() {
        // `update T set Name='hi' --all-rows` — walker covers it
        // all end-to-end; the per-byte class slice carries each
        // node's contribution.
        let runs = highlight_runs("update T set Name='hi' --all-rows");
        let classes: Vec<HighlightClass> = runs.iter().map(|c| c.class).collect();
        assert!(classes.contains(&HighlightClass::Keyword));
        assert!(classes.contains(&HighlightClass::Identifier));
        assert!(classes.contains(&HighlightClass::String));
        assert!(classes.contains(&HighlightClass::Punct));
        assert!(classes.contains(&HighlightClass::Flag));
    }

    #[test]
    fn utf8_unknown_char_advances_one_codepoint() {
        // ✓ is a 3-byte UTF-8 codepoint; the fallback emits a
        // 3-byte Error span (not three 1-byte spans).
        let runs = run("✓");
        assert_eq!(runs.len(), 1);
        assert_eq!(runs[0].2, HighlightClass::Error);
        assert_eq!(runs[0].1 - runs[0].0, "✓".len());
    }

    #[test]
    fn string_with_multi_byte_unicode_classified_as_string() {
        // 'café' is a single string literal; the walker doesn't
        // engage here (no `'café'` entry keyword), so the fallback
        // scans and classifies as String.
        let runs = run("'café'");
        assert_eq!(runs.len(), 1);
        assert_eq!(runs[0].2, HighlightClass::String);
        assert_eq!(runs[0].1, "'café'".len());
    }

    // ---- ADR-0030 §8 / ADR-0032 — SQL keyword highlighting ----

    fn run_advanced(input: &str) -> Vec<(usize, usize, HighlightClass)> {
        highlight_runs_in_mode(input, crate::mode::Mode::Advanced)
            .into_iter()
            .map(|c| (c.start, c.end, c.class))
            .collect()
    }

    #[test]
    fn sql_select_keywords_classified() {
        // ADR-0030 §8 — `select` / `from` get keyword class in
        // Advanced mode (Simple mode gates SELECT out at the
        // dispatcher, so only the entry word would highlight).
        let runs = run_advanced("select * from t");
        assert!(
            runs.iter().any(|(s, e, c)| {
                *c == HighlightClass::Keyword && (*s, *e) == (0, 6)
            }),
            "expected `select` keyword span 0..6; got {runs:?}",
        );
        assert!(
            runs.iter().any(|(s, e, c)| {
                *c == HighlightClass::Keyword && (*s, *e) == (9, 13)
            }),
            "expected `from` keyword span 9..13; got {runs:?}",
        );
    }

    #[test]
    fn sql_expression_operators_classified_as_keywords() {
        // ADR-0031 §5: LIKE / BETWEEN / IN / IS / AND / OR / NOT
        // are part of the predicate ladder. Walker matches them
        // as Word nodes; highlight class = Keyword.
        let input = "select * from t where a like 'x' and b between 1 and 5";
        let runs = run_advanced(input);
        let keywords: Vec<&str> = runs
            .iter()
            .filter(|(_, _, c)| *c == HighlightClass::Keyword)
            .map(|(s, e, _)| &input[*s..*e])
            .collect();
        assert!(keywords.contains(&"like"), "no `like`; got {keywords:?}");
        assert!(keywords.contains(&"and"), "no `and`; got {keywords:?}");
        assert!(
            keywords.contains(&"between"),
            "no `between`; got {keywords:?}",
        );
    }

    #[test]
    fn sql_case_expression_keywords_classified() {
        let input = "select case when a = 1 then 'one' else 'other' end from t";
        let runs = run_advanced(input);
        let keywords: Vec<&str> = runs
            .iter()
            .filter(|(_, _, c)| *c == HighlightClass::Keyword)
            .map(|(s, e, _)| &input[*s..*e])
            .collect();
        for kw in ["case", "when", "then", "else", "end"] {
            assert!(
                keywords.contains(&kw),
                "missing `{kw}` keyword; got {keywords:?}",
            );
        }
    }

    #[test]
    fn sql_dml_keywords_classified() {
        // ADR-0030 §8 / ADR-0033 — the DML entry words and clause
        // keywords (INSERT / INTO / VALUES / ON / CONFLICT /
        // RETURNING / UPDATE / SET / DELETE / FROM) all get the
        // Keyword class in Advanced mode. 3k cross-cut: the
        // ambient highlighter covers the DML surface, not just
        // SELECT.
        let keywords_of = |input: &'static str| -> Vec<&'static str> {
            run_advanced(input)
                .into_iter()
                .filter(|(_, _, c)| *c == HighlightClass::Keyword)
                .map(|(s, e, _)| &input[s..e])
                .collect()
        };

        let insert = keywords_of(
            "insert into t (a) values (1) on conflict (a) do update set a = excluded.a returning a",
        );
        for kw in ["insert", "into", "values", "on", "conflict", "do", "update", "set", "returning"] {
            assert!(insert.contains(&kw), "INSERT/UPSERT: missing `{kw}`; got {insert:?}");
        }

        let update = keywords_of("update t set a = 1 where id = 2 returning a");
        for kw in ["update", "set", "where", "returning"] {
            assert!(update.contains(&kw), "UPDATE: missing `{kw}`; got {update:?}");
        }

        let delete = keywords_of("delete from t where id = 1 returning *");
        for kw in ["delete", "from", "where", "returning"] {
            assert!(delete.contains(&kw), "DELETE: missing `{kw}`; got {delete:?}");
        }
    }
}