//! 为 result(call) 选择唯一且名义身份匹配的 choice。
//! 仅载荷形状相同不足以匹配业务错误；数值 Fault 不进入捕获集合。

use crate::compiler::{check::Context, model::*};
use crate::syntax::{ast, diagnostic::Diagnostic};
use std::collections::BTreeMap;

impl Context<'_> {
    pub(crate) fn capture(
        &mut self,
        call: &ast::Expression,
        expected: Option<&Type>,
        source: &ast::Expression,
    ) -> Result<Expression, Diagnostic> {
        let target = match expected {
            Some(Type::Optional(inner)) => Some(inner.as_ref()),
            expected => expected,
        };
        // 泛型解码直接使用结果 Choice 的成功字段作为类型上下文，不生成包装函数。
        let decoded = if matches!(&call.kind, ast::ExpressionKind::Call(target, _)
            if target.path().as_deref() == Some("dever.json.decode"))
        {
            let Some(Type::Named(index)) = target else {
                return Err(self.error(
                    source,
                    "result(dever.json.decode(...)) requires an explicit result choice",
                ));
            };
            let Shape::Choice(variants) = &self.definitions[*index].shape else {
                return Err(self.error(source, "JSON decode result requires a choice"));
            };
            let mut successes = variants.iter().filter(|variant| !variant.error);
            let (Some(success), None) = (successes.next(), successes.next()) else {
                return Err(self.error(
                    source,
                    "JSON decode result requires exactly one success variant",
                ));
            };
            let [(_, kind)] = success.fields.as_slice() else {
                return Err(self.error(source, "JSON decode success variant requires one value"));
            };
            Some(kind.clone())
        } else {
            None
        };
        let value = self.expression(call, decoded.as_ref())?;
        let decoded_failure;
        let (origin, failures) = match &value.kind {
            Node::Call(function, _) => {
                let signature = &self.signatures[*function];
                (signature.source, signature.failures.as_slice())
            }
            Node::Json(JsonOperation::Decode { error }, _) => {
                decoded_failure = [Failure {
                    definition: *error,
                    variant: 1,
                }];
                (self.definitions[*error].source, decoded_failure.as_slice())
            }
            _ => {
                return Err(self.error(
                    source,
                    "result requires a function call or typed JSON decode",
                ));
            }
        };
        let mut candidates = Vec::new();
        for (index, definition) in self.definitions.iter().enumerate() {
            if definition.source != self.source && !self.definition_names.exported(index) {
                continue;
            }
            if target.is_none()
                && definition.source != self.source
                && definition.source != origin
                && !failures.iter().any(|failure| failure.definition == index)
            {
                continue;
            }
            if target.is_some_and(|kind| *kind != Type::Named(index)) {
                continue;
            }
            let Shape::Choice(variants) = &definition.shape else {
                continue;
            };
            let successes = variants
                .iter()
                .enumerate()
                .filter(|(_, variant)| !variant.error)
                .collect::<Vec<_>>();
            let [(success, variant)] = successes.as_slice() else {
                continue;
            };
            let outputs_match = match &value.value_type {
                Type::Unit => variant.fields.is_empty(),
                Type::Outputs(outputs) => variant
                    .fields
                    .iter()
                    .map(|(_, kind)| kind)
                    .eq(outputs.iter().map(|(_, kind)| kind)),
                kind => matches!(variant.fields.as_slice(), [(_, field)] if field == kind),
            };
            if !outputs_match {
                continue;
            }
            if let Some(targets) = targets(index, variants, failures, self.definitions) {
                candidates.push((index, *success, targets));
            }
        }
        if candidates.len() != 1 {
            return Err(Diagnostic::new(
                "C005",
                "result needs one unambiguous choice with matching success outputs and all declared errors",
                source.span,
            ));
        }
        let (definition, success, targets) = candidates.pop().unwrap();
        let capture = Capture {
            call: value,
            definition,
            success,
            targets,
        };
        self.coerce(
            Expression {
                kind: Node::Capture(Box::new(capture)),
                value_type: Type::Named(definition),
                span: source.span,
            },
            expected,
        )
    }
}

fn targets(
    index: usize,
    variants: &[Variant],
    actual: &[Failure],
    definitions: &[Definition],
) -> Option<Vec<(Failure, usize, bool)>> {
    let mut mapping = BTreeMap::new();
    for (position, variant) in variants.iter().enumerate().filter(|(_, value)| value.error) {
        let direct = Failure {
            definition: index,
            variant: position,
        };
        if actual.contains(&direct) {
            mapping.insert(direct, (position, false));
        }
        if let [(_, Type::Named(inner))] = variant.fields.as_slice()
            && let Shape::Choice(_) = &definitions[*inner].shape
        {
            for failure in actual.iter().filter(|failure| failure.definition == *inner) {
                if mapping.insert(*failure, (position, true)).is_some() {
                    return None;
                }
            }
        }
    }
    actual
        .iter()
        .map(|failure| {
            mapping
                .get(failure)
                .map(|(variant, wrapped)| (*failure, *variant, *wrapped))
        })
        .collect()
}