--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/src/SbpOperators/boundary_conditions/boundary_condition.jl	Sat Jan 11 10:19:47 2025 +0100
@@ -0,0 +1,62 @@
+"""
+    BoundaryCondition
+
+Description of a boundary condition. Implementations describe the kind of
+boundary condition, what boundary the condition applies to, and any associated
+data. Should implement [`boundary`](@ref) and may implement
+[`boundary_data`](@ref) if applicable.
+
+For examples see [`DirichletCondition`](@ref) and [`NeumannCondition`](@ref)
+"""
+abstract type BoundaryCondition end
+
+"""
+    boundary(::BoundaryCondition)
+
+The boundary identifier of the BoundaryCondition.
+"""
+function boundary end
+
+"""
+    boundary_data(::BoundaryCondition)
+
+If implemented, the data associated with the BoundaryCondition.
+"""
+function boundary_data end
+
+"""
+    discretize_data(grid, bc::BoundaryCondition)
+
+The data of `bc` as a lazily evaluated grid function on the boundary grid
+specified by `boundary(bc)`.
+"""
+function discretize_data(grid, bc::BoundaryCondition)
+    return eval_on(boundary_grid(grid, boundary(bc)), boundary_data(bc))
+end
+
+"""
+    DirichletCondition{DT,BID}
+
+A Dirichlet condition with `data::DT` on the boundary
+specified by the boundary identifier `BID`.
+"""
+struct DirichletCondition{DT,BID} <: BoundaryCondition
+    data::DT
+    boundary::BID
+end
+boundary_data(bc::DirichletCondition) = bc.data
+boundary(bc::DirichletCondition) = bc.boundary
+
+"""
+    NeumannCondition{DT,BID}
+
+A Neumann condition with `data::DT` on the boundary
+specified by the boundary identifier `BID`.
+"""
+struct NeumannCondition{DT,BID} <: BoundaryCondition
+    data::DT
+    boundary::BID
+end
+boundary_data(bc::NeumannCondition) = bc.data
+boundary(bc::NeumannCondition) = bc.boundary
+