use crate::{
    config::{BenchmarkConfig, Config},
    error::{self, ConfigError},
};
use miette::{NamedSource, SourceSpan};
use std::path::Path;

/// Validate the configuration after parsing.
pub fn validate_config(config: &Config, content: &str, path: &Path) -> error::Result<()> {
    if config.benchmarks.is_empty() {
        return Err(ConfigError::EmptyBenchmarks {
            src: NamedSource::new(path.display().to_string(), content.to_string()),
        }
        .into());
    }

    for (idx, benchmark) in config.benchmarks.iter().enumerate() {
        validate_benchmark(benchmark, idx, content, path)?;
    }

    Ok(())
}

/// Validate a single benchmark configuration.
fn validate_benchmark(
    benchmark: &BenchmarkConfig,
    idx: usize,
    content: &str,
    path: &Path,
) -> error::Result<()> {
    let src = NamedSource::new(path.display().to_string(), content.to_string());

    validate_positive_field(src.clone(), content, idx, "payload", benchmark.payload)?;
    validate_positive_field(src.clone(), content, idx, "iters", benchmark.iters)?;
    validate_positive_field(src, content, idx, "concurrency", benchmark.concurrency)?;

    Ok(())
}

fn validate_positive_field(
    src: NamedSource<String>,
    content: &str,
    idx: usize,
    field_name: &str,
    value: u32,
) -> error::Result<()> {
    if value == 0 {
        return Err(ConfigError::ValidationError {
            src,
            span: find_field_span(content, idx, field_name),
            field: field_name.into(),
            idx,
            message: "Must be greater than 0".into(),
        }
        .into());
    }
    Ok(())
}

/// Find the span of a field in the TOML content for better error reporting.
fn find_field_span(content: &str, benchmark_idx: usize, field_name: &str) -> Option<SourceSpan> {
    let benchmark_section = find_benchmakr_section(content, benchmark_idx)?;
    find_field_in_section(content, benchmark_section, field_name)
}

fn find_benchmakr_section(content: &str, target_idx: usize) -> Option<(usize, usize)> {
    let mut current_idx = 0;
    let mut section_start = None;
    let mut byte_offset = 0;

    for line in content.lines() {
        let line_len = line.len() + 1; // +1 for newline

        if line.trim_start().starts_with("[[benchmarks]]") {
            if current_idx == target_idx {
                section_start = Some(byte_offset);
            } else if section_start.is_some() {
                return Some((section_start?, byte_offset));
            }
            current_idx += 1;
        }
        byte_offset += line_len;
    }
    section_start.map(|start| (start, content.len()))
}

fn find_field_in_section(
    content: &str,
    (start, end): (usize, usize),
    field_name: &str,
) -> Option<SourceSpan> {
    let section = &content[start..end];
    let mut byte_offset = start;

    for line in section.lines() {
        let line_len = line.len() + 1; // +1 for newline
        if line.trim_start().starts_with('[') && byte_offset != start {
            break;
        }

        if let Some(span) = extract_field_value_span(line, field_name, byte_offset) {
            return Some(span);
        }

        byte_offset += line_len;
    }

    None
}

fn extract_field_value_span(
    line: &str,
    field_name: &str,
    line_offset: usize,
) -> Option<SourceSpan> {
    let eq_idx = line.find('=')?;
    let field = line[..eq_idx].trim();

    if field != field_name {
        return None;
    }

    let after_eq = &line[eq_idx + 1..];
    let value_start_offset = after_eq.len() - after_eq.trim_start().len();
    let value_str = after_eq.trim_start();

    let value_start = line_offset + eq_idx + 1 + value_start_offset;
    let value_len = calculate_value_len(value_str);

    Some(SourceSpan::new(value_start.into(), value_len))
}

fn calculate_value_len(value_str: &str) -> usize {
    if let Some(stripped) = value_str.strip_prefix('"') {
        return stripped.find('"').map_or(value_str.len(), |i| i + 2);
    }

    value_str.find('#').map_or_else(
        || value_str.trim_end().len(),
        |i| value_str[..i].trim_end().len(),
    )
}