//! Diagnostics conversion from Storybook errors to LSP diagnostics

use tower_lsp::lsp_types::{
    Diagnostic,
    DiagnosticSeverity,
    Position,
    Range,
};

use crate::syntax::lexer::{
    Lexer,
    Token,
};

/// Compute diagnostics for a document
pub fn compute_diagnostics(text: &str) -> Vec<Diagnostic> {
    let mut diagnostics = Vec::new();

    // Try to parse the document
    // For now, we'll do a simple check - a real implementation would use the full
    // parser
    match try_parse(text) {
        | Ok(_) => {
            // No syntax errors
        },
        | Err(errors) => {
            for error in errors {
                diagnostics.push(error);
            }
        },
    }

    diagnostics
}

/// Attempt to parse the document and return diagnostics
fn try_parse(text: &str) -> Result<(), Vec<Diagnostic>> {
    // TODO: Integrate with actual parser
    // For now, return Ok for all documents
    // This will be implemented when we add Span tracking

    // Simple placeholder: check for common syntax errors using lexer tokens
    let mut errors = Vec::new();

    // Track brace nesting level and position of each brace
    let mut nesting_stack: Vec<usize> = Vec::new(); // Stack of opening brace positions

    let lexer = Lexer::new(text);

    for (offset, token, _end) in lexer {
        match token {
            | Token::LBrace => {
                nesting_stack.push(offset);
            },
            | Token::RBrace => {
                if nesting_stack.is_empty() {
                    // Unexpected closing brace - no matching opening brace
                    let pos = byte_offset_to_position(text, offset);
                    errors.push(Diagnostic {
                        range: Range {
                            start: pos,
                            end: Position {
                                line: pos.line,
                                character: pos.character + 1,
                            },
                        },
                        severity: Some(DiagnosticSeverity::ERROR),
                        code: None,
                        source: Some("storybook".to_string()),
                        message: "Unexpected closing brace".to_string(),
                        related_information: None,
                        tags: None,
                        code_description: None,
                        data: None,
                    });
                } else {
                    nesting_stack.pop();
                }
            },
            | _ => {},
        }
    }

    // Note: We don't report unclosed braces (nesting_stack not empty)
    // because those are common in incomplete/in-progress code

    if errors.is_empty() {
        Ok(())
    } else {
        Err(errors)
    }
}

fn byte_offset_to_line(text: &str, offset: usize) -> usize {
    let mut line = 0;
    let mut current_offset = 0;

    for ch in text.chars() {
        if current_offset >= offset {
            break;
        }

        if ch == '\n' {
            line += 1;
        }

        current_offset += ch.len_utf8();
    }

    line
}

/// Convert a byte offset to line/column position
/// This is a placeholder - will be replaced when we have proper Span tracking
pub fn byte_offset_to_position(text: &str, offset: usize) -> Position {
    let mut line = 0;
    let mut character = 0;
    let mut current_offset = 0;

    for ch in text.chars() {
        if current_offset >= offset {
            break;
        }

        if ch == '\n' {
            line += 1;
            character = 0;
        } else {
            character += 1;
        }

        current_offset += ch.len_utf8();
    }

    Position {
        line: line as u32,
        character: character as u32,
    }
}

/// Create a diagnostic from a span and message
pub fn create_diagnostic(
    text: &str,
    start: usize,
    end: usize,
    message: String,
    severity: DiagnosticSeverity,
) -> Diagnostic {
    Diagnostic {
        range: Range {
            start: byte_offset_to_position(text, start),
            end: byte_offset_to_position(text, end),
        },
        severity: Some(severity),
        code: None,
        source: Some("storybook".to_string()),
        message,
        related_information: None,
        tags: None,
        code_description: None,
        data: None,
    }
}